Lubricating oil composition, method for producing same and vacuum apparatus

ABSTRACT

A lubricating oil composition is provided, including a fullerene and a base oil, in which the fullerene is a fullerene sublimate, and the base oil is a multiply alkylated cyclopentane oil or an ionic liquid.

TECHNICAL FIELD

The present invention relates to a lubricating oil composition, a methodfor producing the same, and a vacuum apparatus.

Priority is claimed on Japanese Patent Application No. 2019-83392, filedApr. 24, 2019, the content of which is incorporated herein by reference.

BACKGROUND ART

Lubricating oil compositions that can be used under high vacuum arerequired to have properties which are different from those of usuallubricating oil compositions, such as a low vapor pressure andsubstantially no inclusion of volatile components.

Patent Document 1 proposes a lubricating oil composition in which aperfluoroalkyl ether (PFAE), tris(2-octyldodecyl)cyclopentane, or thelike having a low vapor pressure is used as a base oil.

Patent Document 2 proposes an antistatic lubricating oil compositioncontaining an antistatic substance selected from ionic liquidsconsisting of a nitrogen onium cation and a weakly coordinatingfluorine-containing organic anion or a weakly coordinatingfluorine-containing inorganic anion, and a lithium compound such aslithium bis(trifluoromethanesulfonyl)imide.

Patent Document 3 proposes a semi-solid lubricating oil compositionconsisting of an ionic liquid which has a low vapor pressure and aconductivity which achieves antistatic.

Patent Document 4 proposes, as a lubricating oil composition having heatresistance and antioxidant properties, a lubricating oil compositioncontaining (a) at least one base oil selected from the group consistingof an ionic liquid and a fluorine-free synthetic oil having a vaporpressure of 1×10⁻⁴ Torr or less at 25° C. and (b) at least one selectedfrom the group consisting of a fullerene compound and carbon particlesby-produced in the production of a fullerene.

CITATION LIST Patent Document

-   Patent Document 1: Japanese Unexamined Patent Application, First    Publication No. H10-140169-   Patent Document 2: Japanese Unexamined Patent Application, First    Publication No. 2005-89667-   Patent Document 3: Japanese Unexamined Patent Application, First    Publication No. 2005-154755-   Patent Document 4: Japanese Unexamined Patent Application, First    Publication No. 2005-336309

SUMMARY OF INVENTION Technical Problem

However, for example, regarding the application of lubricating oil usedin outer space, it is expected that the physical properties of thelubricating oil composition of any of the aforementioned proposals willchange, as the lubricating oil compositions are placed in a harshenvironment where they are exposed to high-energy rays such as cosmicrays under high vacuum. Accordingly, the proposals are not sufficient tostably maintain lubricating performance over a long period of time.

More specifically, the change in physical properties of a lubricatingoil composition occurs because molecules of a base oil constituting thelubricating oil composition are gradually cleaved and molecular chainsof the base oil are shortened. In particular, in a lubricating oilcomposition used under high vacuum, an increase in vapor pressure of thelubricating oil composition is caused by production of components havinga small molecular weight. This increase in vapor pressure causes variousproblems as described below. The series of changes of a base oil iscalled “deterioration of a base oil”. The deterioration of a base oilmay be caused not only by high-energy rays but also by heat generationdue to frictional wear in a case where an extreme force is applied to asliding portion.

Due to the increase in vapor pressure caused by the deterioration of abase oil, some of the base oil may evaporate and be lost during use, andthe amount of lubricating oil in a sliding portion may decrease. As aresult, the sliding portion becomes worn, which may cause seizure. Inaddition, when some of the base oil evaporates, lubricating oil may alsobe dispersed and adhere to portions other than a sliding portion of amechanical device, thereby contaminating the mechanical device.

In addition, in the lubricating oil composition containing a fullerene,although various lubrication characteristics have been improved, thevapor pressure thereof at an initial stage of use could not be loweredto the same extent as that of a base oil. The reason the vapor pressureof the lubricating oil composition at an initial stage of use is high isthought to be due to the influence of residues of a volatile componentsuch as organic solvents because such a volatile component is usuallyused in a step of producing a fullerene.

An object of the present invention is to provide a lubricating oilcomposition which has a low vapor pressure and in which excellentabrasion resistance can be exhibited, an increase in vapor pressure dueto deterioration of a base oil can be suppressed, and lubricatingperformance can be stably maintained over a long period of time evenunder vacuum; a method for producing the same; and a vacuum apparatus.

Solution to Problem

A first aspect of the present invention is the following lubricating oilcomposition. [1] A lubricating oil composition, including a fullereneand a base oil, in which the fullerene is a fullerene sublimate, and thebase oil is a multiply alkylated cyclopentane oil or an ionic liquid.

The first aspect of the present invention preferably includescharacteristics described in [2] below.

[2] The lubricating oil composition according to [1] above, furtherincluding: a fullerene adduct, wherein the fullerene adduct has astructure in which an additional group has been added to the fullerene,wherein the additional group has a part of a molecular structure whichconstitutes the base oil.

A second aspect of the present invention is the following method forproducing a lubricating oil composition.

[3] A method for producing the lubricating oil composition according to[1] or [2] above, the method including: a dissolution step of dissolvinga fullerene sublimate in a base oil to obtain a fullerene solution.

The second aspect of the present invention preferably includescharacteristics described in [4] to [14] below. The followingcharacteristics are preferably combined with each other.

[4] The method for producing a lubricating oil composition according to[3] above, the method further including: a sublimation step ofsublimating and vaporizing a raw material fullerene in a non-oxidizingatmosphere, and then cooling and solidifying the vaporized fullerene toobtain the fullerene sublimate before the dissolution step.

[5] The method for producing a lubricating oil composition according to[3] or [4] above, in which the fullerene sublimate contains C₆₀ or C₇₀or a mixture thereof.

[6] The method for producing a lubricating oil composition according toany one of [3] to [5], the method further including: a removal step ofremoving insoluble components from the fullerene solution after thedissolution step.

[7] The method for producing a lubricating oil composition according toany one of [3] to [6] above, the method further including: a heattreatment step of subjecting the fullerene solution to a heat treatmentin a non-oxidizing atmosphere after the dissolution step to produce afullerene adduct.

[8] The method for producing a lubricating oil composition according to[7] above, in which a temperature during the heat treatment in the heattreatment step is within a range of higher than an upper limit usagetemperature of the base oil and lower than or equal to the upper limitusage temperature+200° C.

[9] The method for producing a lubricating oil composition according to[7] above, in which a temperature of the heat treatment in the heattreatment step is 150° C. to 300° C.

[10] The method for producing a lubricating oil composition according toany one of [3] to [6] above, the method further including: a radiationtreatment step of irradiating the fullerene solution with radiation in anon-oxidizing atmosphere after the dissolution step to produce afullerene adduct, in which the radiation is ultraviolet light orionizing radiation.

[11] The method for producing a lubricating oil composition according to[10] above, in which the radiation is ultraviolet light having awavelength of 190 nm to 365 nm. [12] The method for producing alubricating oil composition according to [10 or [11] above, in which theamount of energy of the radiation emitted in the radiation treatmentstep is 1 J to 100 J per milliliter of the fullerene solution.

[13] The method for producing a lubricating oil composition according toany one of [7] to [12] above, in which an oxygen partial pressure in thenon-oxidizing atmosphere is less than or equal to 10 pascals.

[14] The method for producing a lubricating oil composition according toany one of [7] to [13] above, in which the heat treatment step or theradiation treatment step is performed until a concentration of thefullerene in the fullerene solution is 0.1 times to 0.7 times aconcentration of the fullerene obtained before the heat treatment stepor the radiation treatment step.

[15] The method for producing a lubricating oil composition according to[14] above, in which a treatment time of the heat treatment step or theradiation treatment step is 5 minutes to 24 hours.

A third embodiment of the present invention is the following vacuumapparatus.

[16] A vacuum apparatus, including: a vacuum container in which thelubricating oil composition according to [1] or [2] above is usedtherein.

Advantageous Effects of Invention

According to the present invention, it is possible to provide alubricating oil composition which has a low vapor pressure and in whichexcellent abrasion resistance can be exhibited, an increase in vaporpressure due to deterioration of a base oil can be suppressed, andlubricating performance can be stably maintained over a long period oftime even under vacuum; a method for producing the same; and a vacuumapparatus.

DESCRIPTION OF EMBODIMENTS

Hereinafter, a lubricating oil composition and a method for producingthe same according to an embodiment of the present invention will bedescribed. The present embodiment is specifically described tofacilitate better understanding of the gist of the invention, and doesnot limit the present invention unless otherwise specified.

Numerical values, orders, times, ratios, materials, amounts,configurations, and the like can be, for example, modified, added,omitted, or replaced within the scope not departing from the gist of thepresent invention.

(Lubricating Oil Composition)

The lubricating oil composition according to the present embodimentincludes a fullerene and a base oil, in which the above-describedfullerene is a fullerene sublimate, and the above-described base oil isa multiply alkylated cyclopentane oil or an ionic liquid. In addition,the lubricating oil composition of the present embodiment may contain afullerene adduct, an additive, and the like to be described below.

(Fullerene Sublimate)

In general, a fullerene production process includes a step of handling afullerene in a volatile organic solvent, for example, extracting afullerene from soot with an organic solvent such as toluene. For thisreason, molecules of the organic solvent are easily incorporated intothe obtained fullerene crystal grains. If such a fullerene is used,volatile components such as molecules of the organic solvent may be alsomixed. Accordingly, a lubricating oil composition having a low vaporpressure cannot be obtained. If the above-described volatile componentsare contained, in a case where, for example, a lubricating oilcomposition is used under high vacuum, the volatile components arevolatilized. At this time, some of a base oil or fullerene are alsoscattered in a liquid state. For this reason, portions other than asliding portion of a mechanical device are contaminated.

In order to prevent this incorporation or contamination, in the presentembodiment, a fullerene substantially free of volatile components isused. That is, the fullerene contained in the lubricating oilcomposition of the present embodiment is a fullerene sublimate. The“fullerene sublimate” is a fullerene substantially free of volatilecomponents. A method for producing a fullerene sublimate will bedescribed in detail in “Sublimation Step” to be described below.

Here, in a case where molecules of an organic solvent are incorporatedinto fullerene crystal grains, the above-described volatile componentsare also incorporated into the crystal grains. For this reason, it isvery difficult to quantitatively analyze the volatile components in thefullerene. Therefore, in the present embodiment, in a case where it canbe stated that the level of increase in a degassing degree describedbelow of a fullerene solution, which is produced by dissolving afullerene sample in a base oil, is substantially 0 (for example, lessthan or equal to 0.1) compared to the base oil, it can be determinedthat this sample is substantially free of volatile components.

Examples of the types of the fullerene included in the fullerenesublimate include C₆₀, C₇₀, high-order fullerenes, and a mixturethereof. Among these fullerenes, C₆₀ or C₇₀ or a mixture thereof ispreferable as the fullerene from the viewpoint of high solubility inlubricating oils. A fullerene mixture, in which 50 mass % or more of C₆₀is contained, is more preferable as the fullerene from the viewpoint ofless brown to black-based discoloration of a lubricating oil (from theviewpoint that deterioration of a lubricating oil composition is easilydetermined by color). The content thereof may be 70 mass % to 100 mass%, or may be 90 mass % to 100 mass %. A fullerene sublimate composed ofonly C₆₀ is still more preferable.

The concentration of the fullerene sublimate in a lubricating oilcomposition can be arbitrarily selected, and is preferably, for example,0.0001 mass % to 0.010 mass %, 0.0005 mass % to 0.008 mass %, 0.001 mass% to 0.005 mass %, or 0.002 mass % to 0.003 mass % as necessary.However, the present invention is not limited to these examples.

(Fullerene Adduct)

The lubricating oil composition of the present embodiment may contain afullerene adduct. The fullerene adduct has a structure in which anadditional group which has a part of a molecular structure constitutingthe above-described base oil is added to the above-described fullerene.

The concentration of the fullerene adduct in a lubricating oilcomposition can be arbitrarily selected, and is preferably, for example,0.0001 mass % to 0.010 mass %, 0.0005 mass % to 0.008 mass %, 0.001 mass% to 0.005 mass %, or 0.002 mass % to 0.003 mass %. However, the presentinvention is not limited to these examples. The concentration of thefullerene adduct may be obtained through an arbitrarily selected method.For example, the concentration thereof may be estimated from thedifference between fullerene concentrations before and after a heattreatment as will be described below.

(Base Oil)

The base oil contained in the lubricating oil composition of the presentembodiment is an oil having a low vapor pressure. Preferred examplesthereof include a multiply alkylated cyclopentane oil or an ionic liquidsuch as dialkylpiperidin bis(trifluoromethanesulfonyl)imide.

It is preferable that no volatile components be contained in the baseoil. Specifically, the base oil has a vapor pressure at 25° C. ofpreferably 1 pascal or less, more preferably 0.1 pascals or less, andparticularly preferably 0.01 pascals or less.

Molecules of a multiply alkylated cyclopentane oil (hereinafter,sometimes referred to as a “MAC oil”) have a structure in which aplurality of alkyl groups are bonded to a cyclopentane ring. The totalnumber of carbon atoms of these alkyl groups is preferably 48 to 112.The total number of carbon atoms may be, for example, 48 to 60, 48 to80, or 70 to 112. The numbers of carbon atoms in each alkyl group may bethe same as or different from each other. The number of alkyl groupsbinding to a cyclopentane ring can also be arbitrarily selected and maybe, for example, 1 to 5, 2 to 4, or 3 or 4. More specific examplesthereof include tris(2-octyldodecyl)cyclopentane to which three alkylgroups having 20 carbon atoms are bonded thereto,tetra(dodecyl)cyclopentane to which four alkyl groups having 12 carbonatoms are bonded thereto, and a mixture thereof. However, the presentinvention is not limited to these examples.

An ionic liquid is an ionic compound which contains a cationic moietyand an anionic moiety, and is particularly preferably a liquid at roomtemperature to 80° C. because in this case it is easy to handle.

Examples of the above-described anionic moieties includebis(trifluoromethanesulfonyl)imide, bis(fluorosulfonyl)imide, anddiethyl phosphate.

In addition, examples of the above-described cationic moieties includelithium, cyclohexyltrimethylammonium, ethyldimethylphenylethylammonium,methyltrioctylammonium, 1-aryl-3-methylimidazolium,1-ethyl-3-methylimidazolium, 1-butyl-3-methylimidazolium,1-hexyl-3-methylimidazolium, 1-butyl-2,3-diethylimidazolium,3,3′-(butane-1,4-diyl) bis(1-vinyl-3-imidazolium),1-decyl-3-methylimidazolium, 1-butyl-4-methylpyridium,4-ethyl-4-methylmorpholinium, tetrabutylphosphonium,tributyl(2-methoxyethyl)phosphonium, trihexyl(tetradecyl)phosphonium,butyl-1-methylpiperidinium, 1-butylpyridium,1-butyl-methylpyrrolidinium, and tributylsulfonium.

Specific examples of ionic liquids include a compound obtained byappropriately combining a compound of the cationic moiety and a compoundof the anionic moiety. The compound of the cationic moiety and thecompound of the anionic moiety to be combined may not limited to be asingle kind. That is, one or more kinds of the compounds may be combinedwith each other.

The amount of base oil in a lubricating oil composition can bearbitrarily selected. For example, the amount thereof may be 90.0000mass % to 99.9999 mass %. However, the present invention is not limitedto these examples.

(Additives)

The lubricating oil composition of the present embodiment can containadditives substantially containing no volatile components within a rangenot impairing the effects of the lubricating oil composition in additionto the base oil, the fullerene sublimate, and the fullerene adduct.Examples of additives include antioxidants, viscosity index improvers,extreme pressure additives, detergent dispersants, pour pointdepressants, corrosion inhibitors, solid lubricants, oiliness improvers,rust preventive additives, anti-emulsifiers, antifoaming agents, andhydrolysis inhibitors which are commercially available. Such additivesmay be used alone or in a combination of two or more thereof. The amountof additives can be arbitrarily selected.

Examples of antioxidants include butylhydroxyanisole (BHA) anddialkyldiphenylamines.

Examples of viscosity index improvers include hydride additives ofpolyalkylstyrenes or styrene-diene copolymers.

Examples of extreme pressure additives include dibenzyl disulfide, anallyl phosphate ester, an allyl phosphite ester, an amine salt of anallyl phosphate ester, an allyl thiophosphate ester, and an amine saltof an allyl thiophosphate ester.

Examples of detergent dispersants include benzylamine succinic acidderivatives, and alkylphenol amines.

Examples of pour point depressants include chlorinatedparaffin-naphthalene condensates, chlorinated paraffin-phenolcondensates, and polyalkylstyrene-based pour point depressants.

Examples of anti-emulsifiers include alkylbenzene sulfonates.

Examples of corrosion inhibitors include dialkylnaphthalene sulfonates.

(Method for Producing Lubricating Oil Composition)

The method for producing a lubricating oil composition of the presentembodiment includes a dissolution step of dissolving the above-describedfullerene sublimate in the above-described base oil to obtain afullerene solution. Although the fullerene solution obtained in thisstep may be used as a lubricating oil composition as it is, a furtherprocessed fullerene solution may be used as a lubricating oilcomposition as described below.

The above-described fullerene sublimate used in the dissolution steppreferably contains C₆₀ or C₇₀ or a mixture thereof from the viewpointof high solubility in the lubricating oil as described above. Afullerene mixture in which 50 mass % or more of C₆₀ is contained is morepreferable from the viewpoint of less discoloration of the lubricatingoil. A fullerene sublimate composed of C₆₀ is still more preferable.

The concentration of a fullerene in a fullerene solution is arbitrarilyselected and is, for example, preferably 1 mass ppm (0.0001 mass %) to100 mass ppm (0.01 mass %), more preferably 3 mass ppm (0.0003 mass %)to 75 mass ppm (0.0075 mass %), and still more preferably 5 mass ppm(0.0005 mass %) to 50 mass ppm (0.005 mass %). The concentration of thefullerene may be measured through an arbitrarily selected method, forexample, a technique using high-performance liquid chromatography(HPLC).

The dissolution in the above-described dissolution step can be performedthrough an arbitrarily selected method and can be preferably performedthrough ordinary mechanical stirring, ultrasonic stirring, or the like.Regarding the temperature, in a case where a base oil is a low-viscosityliquid at room temperature, the base oil can be stirred at roomtemperature. On the other hand, in a case where a base oil is ahigh-viscosity liquid or solid at room temperature, the base oil ispreferably turned into a low-viscosity liquid through heating, and thenis stirred to perform dissolution. The stirring time may be arbitrarilyselected.

(Sublimation Step)

The above-described fullerene sublimate used in the dissolution step maybe commercially available products or may be produced using ordinaryfullerenes (raw material fullerene) by providing a sublimation step.That is, the above-described method for producing a lubricating oilcomposition may further include a sublimation step of sublimating andvaporizing a raw material fullerene in a non-oxidizing atmosphere beforethe dissolution step, and then cooling and solidifying the vaporizedfullerene to obtain the above-described fullerene sublimate. Forexample, a raw material fullerene can be sublimated and vaporized in anon-oxidizing atmosphere in which the oxygen gas partial pressure isless than or equal to 10 pascals to form a gas, and can then be cooledand solidified to obtain the above-described fullerene sublimate. Theraw material fullerene may mean fullerenes which are not obtained in thesublimation step, and commercially available products may be used.

By providing the sublimation step, the dissolution step can be performedcontinuously after the sublimation step. This method is preferable fromthe viewpoint of preventing incorporation of volatile components fromair or the like by avoiding storage of the obtained fullerene sublimate.

In the sublimation step, specifically, a raw material fullerene can besublimated using, for example, a commercially available sublimationpurification device. As an example of sublimation, a raw materialfullerene is first placed in a heating unit inside a sublimationpurification device, and the inside of the device is depressurized inthis state to reduce the oxygen gas partial pressure to 10 pascals orless. After the depressurization, the heating unit is heated to change aphase of the raw material fullerene in the heating unit from a solid toa gas. Thereafter, the raw material fullerene is phase-changed from agas to a solid through cooling and precipitated as a fullerenesublimate. According to this method, since the raw material fullerene istemporarily in a gas molecule state, volatile components contained incrystals of the raw material fullerene can be removed. The fullerenesublimate obtained in this manner does not substantially contain thevolatile components. Accordingly, by providing the sublimation step, alubricating oil composition having a low vapor pressure can be obtained.

(Removal Step)

The fullerene solution obtained in the dissolution step sometimescontains insoluble fullerenes or the like. In this case, these insolublecomponents are preferably removed. That is, the above-described methodfor producing a lubricating oil composition may further include aremoval step of removing insoluble components from the above-describedfullerene solution after the above-described dissolution step. Methodsfor removing insoluble components can be arbitrarily selected, andexamples thereof include a method for performing filtering with amembrane filter, a method for performing precipitation and removal usinga centrifuge, and a method of using both methods in combination.

(Heat Treatment Step/Radiation Treatment Step)

A fullerene adduct can be obtained by subjecting the above-describedfullerene solution to a heat treatment or a radiation treatment in anon-oxidizing atmosphere in which the oxygen partial pressure islowered, for example. That is, the above-described method for producinga lubricating oil composition may further include a heat treatment stepof subjecting the above-described fullerene solution to a heat treatmentin a non-oxidizing atmosphere after the above-described dissolution stepto produce the above-described fullerene adduct. In addition, the methodthereof may further include a radiation treatment step of irradiatingthe above-described fullerene solution with radiation in a non-oxidizingatmosphere after the above-described dissolution step to produce theabove-described fullerene adduct.

The fullerene adduct may be obtained by performing one or both of theheat treatment step and the radiation treatment step or may be obtainedby performing both of the heat treatment step and the radiationtreatment step at the same time.

By performing such treatments, a part of a molecular structureconstituting a base oil is cleaved, and as a result, highly reactivemolecules (hereinafter, sometimes simply referred to as “cleavedmolecules”) are produced. The cleaved molecules are added to a fullereneto produce a fullerene adduct. The fullerene adduct obtained throughthese treatments has a structure in which an additional group which hasa part of a molecular structure constituting the above-described baseoil has been added to the fullerene. An excellent effect can be obtainedthrough the production of the fullerene adduct.

The change of the fullerene to the fullerene adduct can be confirmed byperforming mass spectrum measurement on the fullerene solution beforeand after the treatments. For example, in a case where C₆₀ is used as afullerene sublimate, only the peak of m/z=720 corresponding to C₆₀ isconfirmed in a lubricating oil composition before performing a heattreatment or a radiation treatment. On the other hand, in a lubricatingoil composition after such treatments, the peak of 720 is reduced insize, and a plurality of peaks of the fullerene adduct appear. As themain peak, a peak (722+2N) corresponding to C₆₀ to which a plurality ofalkyl groups having different chain lengths have been added can beconfirmed. N represents a natural number of 60 or less. The peaks showthat two alkyl radical molecules produced through cleavage of a base oilhave been added to C₆₀.

Since the molecules of the above-described base oil are not necessarilycleaved at a specific site, the fullerene adduct is not usually composedof a single type of molecule, and their analysis is difficult. For thisreason, regarding the progress of the reaction in which the fullereneadduct is produced, the concentration of the remaining fullerene may bemeasured and the fullerene residual rate represented by the followingequation may be used as a guideline.

Fullerene residual rate)=[concentration of fullerene aftertreatments]/[concentration of fullerene before treatments]

In the above-described equation, the treatments mean one or both of theheat treatment and the radiation treatment. In order to obtain afullerene residual rate in the middle of treatments, the “concentrationof fullerene after treatments” above may be replaced with “concentrationof fullerene during treatments”. In addition, the concentration of thefullerene can be measured through a technique using high-performanceliquid chromatography (HPLC) described in examples.

The concentration of the fullerene adduct produced may be estimated bythe following approximate equation.

[Concentration of fullerene adduct]≅[concentration of fullerene beforetreatments]/[concentration of fullerene after treatments]

The fullerene residual rate obtained by the above-described approximateequation is preferably 0.1 to 0.7 and more preferably 0.2 to 0.5. If theabove-described fullerene residual rate is 0.1 to 0.7, the lubricity ofa lubricating oil composition can be more stably expressed from theinitial stage of use, frictional wear of a sliding portion of amechanical device can be suppressed, and production of volatilecomponents due to deterioration of a base oil can be suppressed.

Accordingly, in the present embodiment, it is preferable that theconcentration of fullerene of a fullerene solution be monitored duringthe heat treatment step or the radiation treatment step, and the heattreatment step or the radiation treatment step be performed until theconcentration of the fullerene in the fullerene solution is 0.1 to 0.7with respect to the concentration of the fullerene before theabove-described heat treatment step or the above-described radiationtreatment step. In addition, the treatment time of the above-describedheat treatment step or the radiation treatment step can be arbitrarilyselected, but is preferably 5 minutes to 24 hours, which facilitates theoperation of the heat treatment or the radiation treatment. Regardingadjustment of the treatment time, for example, the treatment time can beshortened by increasing the heat treatment temperature or theirradiation intensity and conversely can be prolonged by lowering theheat treatment temperature or the irradiation intensity. In addition, inthe radiation treatment step, the radiation intensity, the irradiationtime, and the number of times of irradiation may be arbitrarilyselected. For example, as a method for setting the concentration of thefullerene to the above-described range, a method of adjusting the numberof times of irradiation, for example, by repeating irradiation withradiation having a relatively high radiation intensity for a shortperiod of time (about 0.1 seconds to 3 minutes) 2 to 10 times, ispreferable since operation thereof is easy.

In general, the fullerene solution is handled in atmospheric air. Forthis reason, the concentration of oxygen gas in the solution is inequilibrium with oxygen gas in atmospheric air. In addition, oxygenmolecules react with cleaved molecules and suppress the production ofthe fullerene adduct. For this reason, it is preferable that as manyoxygen molecules in the fullerene solution be removed as possible and aheat treatment or a radiation treatment be performed in a non-oxidizingatmosphere. Regarding the above-described non-oxidizing atmosphere in aheat treatment step or a radiation treatment step, the oxygen partialpressure in the above-described non-oxidizing atmosphere in a gas phasein equilibrium with the fullerene solution is preferably less than orequal to 10 pascals, more preferably less than or equal to 5 pascals,and still more preferably less than or equal to 2 pascals. The oxygenpartial pressure may be less than or equal to 1 pascal or less than orequal to 0.1 pascals. In addition, preferred examples of non-oxidizingatmospheres include an inert gas atmosphere as described below.

Specific examples of the heat treatment step can include the followingtwo methods, and specific examples of the radiation treatment step caninclude the following one method.

Heat Treatment Step

The above-described heat treatment is preferably performed at atemperature exceeding the upper limit of the usage temperature of a baseoil. When the upper limit usage temperature of a base oil is exceeded,cleaved molecules are likely to be produced. Furthermore, the higher thetemperature, the more cleaved molecules are produced. As a result, theheat treatment time may be short. From the viewpoint of heat treatmenttime for easy operation, it is preferable that the temperature of theheat treatment in this heat treatment step be within a range of higherthan an upper limit usage temperature of a base oil and lower than orequal to the upper limit usage temperature +200° C. of a base oil. Theupper limit usage temperature of a base oil can be ascertained from thecatalog or the like of a base oil manufacturer. The upper limit usagetemperature may mean the upper limit of the temperature of a base oil atwhich the base oil can be relatively stably used. In a case where theupper limit usage temperature of the base oil is unclear, as aguideline, the heat treatment temperature is preferably 150° C. to 300°C. and more preferably 200° C. to 250° C. The time for the heattreatment step can be arbitrarily selected, but is preferably 5 minutesto 24 hours. The time may be 5 minutes to 30 minutes, 30 minutes to 1hour, 1 hour to 5 hours, 5 hours to 24 hours, or the like. However, thepresent invention is not limited to these examples.

The method for creating a non-oxidizing atmosphere can be arbitrarilyselected. For example, a fullerene solution may be accommodated in anairtight container made of a metal such as stainless steel, and then thecontainer may be sealed. Subsequently, the inside of the container maybe purged with an inert gas such as nitrogen gas or argon gas and aninert gas may also be bubbled into the fullerene solution in thecontainer. In this manner, an equilibrium is created between thefullerene solution and the inert gas, and the above-described oxygenpartial pressure is set to less than or equal to 10 pascals.

Alternatively, examples of the method for creating a non-oxidizingatmosphere also include a method for depressurizing the inside of anairtight container. For example, if the inside of the container isdepressurized to 10 pascals or less, the oxygen partial pressure of agas phase can be set to 10 pascals or less, usually 2 pascals or less.When a non-oxidizing atmosphere is created through depressurization ofthe inside of a container in this manner and the container is heatedwhile the state is maintained, a fullerene solution can be heat-treated.

The fullerene solution can be heated through an arbitrarily selectedmethod. For example, the heating can be performed through a method ofperforming heating from outside with an oil bath, a method forperforming irradiation with infrared light, or a method for performingirradiation with microwaves.

In addition, in the heat treatment step, the fullerene residual rate maybe checked every time a certain period of time elapses and heating (heattreatment) may be continued until a desired fullerene residual rate isobtained.

Radiation Treatment Step

The radiation used in the above-described radiation treatment isradiation having energy to produce cleaved molecules. Specifically, theradiation is ultraviolet light or ionizing radiation and is preferablyultraviolet light. The radiation is more preferably ultraviolet lighthaving a wavelength of 190 nm to 365 nm and still more preferablyultraviolet light having a wavelength of 330 mn to 350 nm. For example,a C—C single bond is cleaved by ultraviolet light having a wavelength of341 nm or less. In addition, in a case of performing an irradiationtreatment at normal temperature, thermal vibration is superimposed, andtherefore, the C—C single bond is cleaved even by ultraviolet lighthaving a wavelength which is slightly longer than 341 nm. Accordingly,sufficient cleaved molecules can be produced through irradiation withultraviolet light having a wavelength of 190 nm to 365 nm. In addition,as long as cleaved molecules can be produced, low-energy radiation ispreferable from the viewpoint of limiting binding sites in base oilmolecules to be cleaved. For this reason, it is thought that relativelylarge cleaved molecules retaining partial shapes of molecules of theoriginal base oil are likely to be obtained, and the affinity betweenthe base oil and the obtained fullerene adduct improves.

The radiation treatment is preferably performed in a non-oxidizingatmosphere similarly to the above-described heat treatment. At the timeof irradiation with radiation, a radiation source such as an ultravioletlamp may be inserted into a container or a container may be used whereinat least a part thereof is made of a material through which radiation tobe used is transmitted in order to irradiate from outside a container.For example, in a case of irradiation with ultraviolet light, the wholeor a part of the above-described stainless steel container can bereplaced with an element made of a material through which ultravioletlight is transmitted such as quartz glass.

The amount of energy of radiation emitted in the radiation treatmentstep can be arbitrarily selected and is, per one milliliter of afullerene solution, preferably 1 J to 100 J, more preferably 1.5 J to 60J, and still more preferably 2 J to 20 J. The amount of energy thereofmay be, for example, 1 J to 10 J and 1 J to 8 J. When the amount iswithin the ranges, the range of the concentration of fullerene aftertreatments which is obtained from the above-described equation, that is,the fullerene residual rate is easily adjusted to 0.1 to 0.7. Asdescribed above, the irradiation may be performed only once, or theirradiation may be performed plural times, for example, may be dividedinto two or more times. The irradiation may be performed under the sameconditions. In a case where the irradiation is performed plural times,the total energy amount of radiation is preferably within theabove-described range. The number of times of irradiation can bearbitrarily selected and may be, for example, within a range of 1 to 10times or a range of 2 to 5 times. However, the present invention is notlimited to these examples. In addition, it is preferable that thefullerene residual rate be checked every time irradiation is performed,and the irradiation be repeated one or more times until a targetfullerene residual rate is obtained.

In a case of irradiation with ultraviolet light, general low-pressuremercury lamps, UV ozone lamps, ultraviolet LEDs, excimer lamps, xenonlamps, and the like can be used. Regarding the irradiation dose ofultraviolet light, the energy density (mW/cm²) of ultravioletirradiation light is previously measured using an ultravioletphotometer, and then the irradiation time (seconds) and the irradiationrange (cm²) are determined. Using the obtained values, the amount ofenergy (J) of ultraviolet light to be emitted can be determined. Theirradiation time can be arbitrarily selected. For example, theirradiation time may be 5 minutes to 24 hours. Alternatively, theirradiation time may be 0.1 seconds to 1 hour, 0.2 seconds to 30minutes, 0.3 seconds to 3 minutes, 0.5 seconds to 60 seconds, or 1second to 30 seconds.

According to the lubricating oil composition of the present embodiment,not only is the frictional resistance reduced and abrasion resistanceexcellent, but also the vapor pressure can be reduced, production ofvolatile components due to deterioration of a base oil can besuppressed, and an increase in vapor pressure of the lubricating oilcomposition can be suppressed. The lubricating oil composition of thepresent embodiment can be used in various applications, but isparticularly suitable for use in a vacuum or in outer space.

Although the preferred embodiment of the present invention has beendescribed in detail above, the present invention is not limited to aspecific embodiment and various modifications and changes can be madewithin the scope of the gist of the present invention disclosed in theclaims.

EXAMPLES

Hereinafter, the present invention will be described in more detailbased on examples, but is not limited to these examples.

Example 1 (Preparation of Lubricating Oil Composition)

First, 10 g of raw material fullerene C₆₀ (manufactured by FrontierCarbon Corporation, Nanom™ Purple ST) was sublimated using a sublimationpurification device (small sublimation purification device manufacturedby Asahi Glassplant inc.) to obtain a fullerene sublimate. Thesublimation of the raw material fullerene was performed in a three-zonesystem. A high-temperature zone was set to 700° C., a medium-temperaturezone was set to 200° C., a low-temperature zone was set to roomtemperature, and the pressure of each zone was set to 10 pascals orless. The raw material fullerene was placed in the high-temperature zoneand phase-changed from a solid to a gas, and solid fullerene sublimatewhich was phase-changed from a gas to a solid was collected from themedium-temperature zone.

Regarding the sublimation operation, the raw material fullerene wasplaced at room temperature, and each zone was depressurized until thepressure was 10 pascals or less. Thereafter, the temperatures of thehigh-temperature zone and the medium-temperature zone weresimultaneously raised to a constant temperature at a rate of 10° C./min.The fullerene sublimation began when the temperature of thehigh-temperature zone was higher than 600° C., and the pressure duringthe sublimation was 10 pascals or less.

Next, 0.001 g of the obtained fullerene sublimate was mixed with 10 g oftris(2-octyldodecyl)cyclopentane (manufactured by Nye Lubricants,Synthetic Oil 2001A), which was a MAC oil as a base oil. The obtainedmixture was stirred with a stirrer at room temperature for 36 hours.Next, this was filtered with a 0.1 μm mesh membrane filter to obtain afullerene solution. The concentration of the fullerene in the obtainedfullerene solution was measured, and the result was 100 mass ppm. Theobtained fullerene solution was used as a lubricating oil composition.

The concentration of the above-described fullerene was measured using ahigh-performance liquid chromatograph (manufactured by AgilentTechnologies, 1200 series). Specifically, using this device, the amountof fullerene in the sample such as a lubricating oil composition wasdetermined by detecting an absorbance (wavelength of 309 nm) using acolumn YMC-Pack ODS-AM (150 mm×4.6) manufactured by YMC CO., LTD. and a1:1 (volume ratio) mixture of toluene and methanol as a developmentsolvent. In addition, a calibration curve was created from theabove-described raw material fullerene.

(Evaluation of Abrasion Resistance)

The abrasion resistance of the obtained lubricating oil composition wasevaluated using an abrasion resistance tester (manufactured by AntonPaar, Ball-On-Disc Tribometer).

First, a substrate and a ball were prepared, and the materials thereofwere set to a high carbon chromium bearing steel material SUJ2. Thediameter of the ball was set to 6 mm. The lubricating oil compositionwas applied to one main surface of the substrate, and the substrate washeated to 100° C. Next, the substrate was rotated and the fixed ball wasslid on the one main surface of the substrate via the lubricating oilcomposition so that the ball drew a concentric orbit on the substrate.The speed of the ball on the one main surface of the substrate was setto 5 cm/sec, and the load of the ball on the one main surface of thesubstrate was set to 10 N. The rubbing surface (circle) of the ballsurface, which was obtained when the sliding distance of the ball on theone main surface of the substrate was 300 m in total, was observed withan optical microscope. The diameter of the rubbing surface formed on theball was measured, and the numerical value was considered as abrasionresistance. It can be said that the smaller the diameter of the rubbingsurface, the better the abrasion resistance. The results are shown inTable 1.

(Evaluation of Stability)

The presence or absence of components which are volatilized from thelubricating oil composition under high vacuum was measured using atemperature-programmed desorption gas analyzer (manufactured by RigakuCorporation, TPD type V). The degree of desorbed gas of 0.01 g of thelubricating oil composition was measured at an atmospheric pressure of10⁻⁵ pascals. In order to eliminate the influence of molecules having amolecular weight smaller than that of carbonic acid gas (molecularweight of 44), an integrated value of peaks of molecular weights of 46to 200 was obtained as a degree of desorbed gas. As a comparativeproduct, a MAC oil to which 1 mass ppm of trimethylbenzene (TMB)(manufactured by Tokyo Chemical Industry Co., Ltd.) has been added as avolatile component was used, and the same measurement was carried out.Peaks due to TMB were detected in the measurement of the MAC oil towhich TMB was added, and the integrated value of the peaks was used as 1(reference value). The ratio of a measured integrated value of peakswhich were originated from the desorbed gas of the lubricating oilcomposition to the reference value was obtained as a degree of desorbedgas. It can be said that the smaller the degree of desorbed gas, thebetter the stability under high vacuum.

The degree of desorbed gas was measured at two points, one before anabrasion resistance test and the other after the abrasion resistancetest. In the above-described abrasion resistance test, a metal wasbrought into direct contact with the sample and heat was generated.Accordingly, molecular chains of a base oil broke and deteriorated. As aresult of the deterioration, some of the broken molecules were detectedas volatile components through the previous method. That is, sincedeterioration of a base oil proceeds in lubricating oil with poorabrasion resistance, the amount of desorbed gas component increases,which is not preferable. The results are shown in Table 1.

Comparative Example 1

A lubricating oil composition was obtained in the same manner as inExample 1 except that raw material fullerene (without sublimation step)was used as it is instead of the fullerene sublimate. The results of thedegree of desorbed gas and the abrasion resistance of the obtainedlubricating oil composition are shown in Table 1.

Comparative Example 2

A lubricating oil composition was obtained in the same manner as inExample 1 except that no fullerene was added to a MAC oil. The resultsof the degree of desorbed gas and the abrasion resistance of theobtained lubricating oil composition are shown in Table 1.

TABLE 1 Degree of desorbed gas from Composition Fullerene lubricatingcomposition of lubricating Treatment for producing residual Diameter[μm] of Before abrasion After abrasion oil composition fullerene adductrate [—] rubbing surface resistance test resistance test Example 1 MACoil + FLN sublimate None 1.0 200 0.1 0.9 Comparative MAC oil + FLNsublimate None 1.0 205 1.0 1.9 Example 1 Comparative MAC oil only None —300 0.1 2.4 Example 2 Example 2 MAC oil + FLN sublimate Ultravioletirradiation (2 0.55 160 0.1 0.5 times) Example 3 MAC oil + FLN sublimateHeating 0.15 155 0.1 0.3 Example 4 MAC oil + FLN sublimate Ultravioletirradiation (8 0.25 155 0.1 0.3 times) Example 5 MAC oil + FLN sublimate185 nm/254 nm 0.22 165 0.1 0.5 wavelengths, for 20 seconds Example 6 MACoil + FLN sublimate X-ray irradiation, for 480 0.20 180 0.1 0.8 secondsExample 7 Ionic liquid + FLN None 1.00 250 0.1 1.0 sublimate ComparativeIonic liquid + FLN None 1.00 250 1.1 2.0 Example 3 Example 8 Ionicliquid + FLN Heating 0.12 200 0.1 0.3 sublimate Example 9 Ionic liquid +FLN Ultraviolet irradiation (8 0.35 210 0.1 0.4 sublimate times) Example10 Ionic liquid + FLN None 1.00 230 0.1 1.0 sublimate Comparative Ionicliquid + FLN None 1.00 230 1.1 2.0 Example 4 Example 11 Ionic liquid +FLN Heating 0.18 190 0.1 0.3 sublimate Example 12 Ionic liquid + FLNUltraviolet irradiation (8 0.40 195 0.1 0.4 sublimate times) Example 13Ionic liquid + FLN None 1.00 220 0.1 0.9 sublimate Comparative Ionicliquid + FLN None 1.00 220 1.0 1.9 Example 5

It can be seen from Table 1 that, when a fullerene solution (lubricatingoil composition) was obtained in Example 1 by dissolving the fullerenesublimate in a MAC oil, the abrasion resistance was excellent becausethe diameter of the rubbing surface was 200 μm. In addition, thedegassing degree of the lubricating oil composition before the abrasionresistance test was 0.1, and it was found that the vapor pressure at aninitial stage of use of the lubricating oil composition was low and thestability under high vacuum at an initial stage of use was excellent.Furthermore, the degassing degree of the lubricating oil compositionafter the abrasion resistance test was 0.9, and it was found that anincrease in vapor pressure due to deterioration of a base oil wassuppressed and the stability under high vacuum was excellent.

In addition, when comparing Example 1 with Comparative Example 1,although both had the same the abrasion resistance, the degrees ofdesorbed gas before and after the abrasion resistance test in Example 1were superior to those of Comparative Example 1. It was inferred thatthis is because the sublimated fullerene (fullerene sublimate)substantially contained no volatile components, and the volatilecomponents contained in the lubricating oil composition were reduced byadding the fullerene sublimate to the MAC oil, and as a result, theamount of desorbed gas could be minimized.

In addition, when comparing Example 1 with Comparative Example 2, bothhad an excellent degassing degree before the abrasion resistance to thesame extent. However, in Comparative Example 2, the abrasion resistancedeteriorated and the degassing degree after the abrasion resistance testwas significantly inferior. From this, it was found that the abrasionresistance was improved by adding the fullerene sublimate to the MACoil, and as a result, the increase in degassing amount was suppressed.

Example 2

A lubricating oil composition was obtained in the same manner as inExample 1 except that the fullerene solution (lubricating oilcomposition) obtained in Example 1 was irradiated with ultravioletlight. The results of the degree of desorbed gas and the abrasionresistance of the obtained lubricating oil composition are shown inTable 1.

The ultraviolet irradiation in Example 2 was performed according to thefollowing procedure. First, 3 mL of the lubricating oil composition wastaken out and added into a septum cap-attached quartz cell (manufacturedby Tokyo Garasu Kikai Co., Ltd., S15-UV-10).

Next, two injection needles were inserted into the septum cap of thequartz cell, and nitrogen gas having a purity of 99.99% (the partialpressure of gases other than nitrogen at normal pressure was 10 pascalsor less) was allowed to flow through one needle at 60 mL/min for 10minutes. Next, the fullerene solution placed in the quartz cell wasintermittently subjected to ultraviolet irradiation.

An ultraviolet irradiation device (manufactured by San-Ei Tech Ltd.,OmniCure 52000) was used for the ultraviolet irradiation. Specifically,the mesh size of a filter was set to 250 nm to 450 nm, the output wasadjusted to 1 W/cm² while measurement was performed using an ultravioletilluminometer (wavelength of 230 nm to 390 nm) within an irradiationrange of 2 cm², and the irradiation timer was set to 1 second. Inaddition, it was set so that 2 J of energy (0.7 J per milliliter of thefullerene solution) could be emitted with one irradiation.

Next, about 0.01 mL of the fullerene solution was sampled from theinside of the quartz cell after every ultraviolet irradiation using aninjector, and the concentration of the fullerene was measured throughhigh-performance liquid chromatography (HPLC) to determine the fullereneresidual rate.

The fullerene residual rate was 0.55 after 2 times of ultravioletirradiation (1.3 J per milliliter of the fullerene solution). Thus, theultraviolet irradiation was stopped and the contents were taken out fromthe quartz cell to obtain a lubricating oil composition. Theconcentration of the fullerene in the lubricating oil composition wasmeasured, and the result was 55 mass ppm. The fullerene residual ratewas 0.55. The results are shown in Table 1.

In addition, the fullerene solution (lubricating oil composition ofExample 1) before the ultraviolet irradiation and the lubricating oilcomposition of Example 2 obtained after the ultraviolet irradiation weresubjected to a component analysis regarding components having amolecular weight of 720 to 2,000 using a mass spectrometer (manufacturedby Agilent Technologies, LC/MS, 6120). In the fullerene solution ofExample 1 before the ultraviolet irradiation, a main peak of 720corresponding to the fullerene and a plurality of other peaks thought tobe caused by a base oil were observed. In the lubricating oilcomposition of Example 2 after the ultraviolet irradiation, peaks ofm/z=750, 764, 766, 778, 780, 792, 794, 796, 808, 806, 820, and 834 werenewly confirmed as main peaks in addition to the above-described peaks.From these findings, it was confirmed that the fullerene solution(lubricating oil composition) after the ultraviolet irradiation includesa fullerene and a fullerene adduct produced. Fullerene solutions beforeand after a heat treatment or a radiation treatment were also analyzedin other examples and comparative examples. As a result, no fullereneadduct was confirmed in the fullerene solutions before the heattreatment or the radiation treatment, but confirmed in the fullerenesolutions after these treatments.

Example 3

A fullerene solution placed in a quartz cell was immersed in an oil bathat 200° C. and heated instead of the ultraviolet irradiation. Alubricating oil composition was obtained in the same manner as inExample 2 except that heating was performed instead of the ultravioletirradiation. The results of the degree of desorbed gas and the abrasionresistance of the obtained lubricating oil composition are shown inTable 1.

In the heating in Example 3, about 0.01 mL of the fullerene solution wassampled from the inside of the quartz cell every 5 minutes using aninjector, and the concentration of the fullerene was measured throughHPLC to determine the fullerene residual rate. The fullerene residualrate 15 minutes after the start of the measurement was 0.2. Thus, thequartz cell was taken out from the oil bath and cooled to roomtemperature to obtain a lubricating oil composition. The concentrationof the fullerene in the lubricating oil composition was measured, andthe result was 15 mass ppm. The fullerene residual rate was 0.15.

As shown in Table 1, in Example 2, when the fullerene solution wasobtained by dissolving the fullerene sublimate in a MAC oil andirradiated with ultraviolet light twice, the diameter of the rubbingsurface was 160 μm and the degassing degrees of the lubricating oilcomposition before and after the abrasion resistance test wererespectively 0.1 and 0.5. That is, it was found that the abrasionresistance and the stability under high vacuum were superior. Similarly,in Example 3, when the fullerene solution was obtained by dissolving thefullerene sublimate in a MAC oil and subjected to heat treatment, thediameter of the rubbing surface was 155 μm and the degassing degrees ofthe lubricating oil composition before and after the abrasion resistancetest were respectively 0.1 and 0.3. That is, it was found that theabrasion resistance and the stability under high vacuum were superior.

In addition, when comparing Examples 2 and 3 in which ultravioletirradiation or heating was performed as a step of producing a fullereneadduct with Example 1 in which the above-described ultravioletirradiation or the heating was not performed, both of the abrasionresistance and the degree of desorbed gas before and after an abrasionresistance test in Examples 2 and 3 were excellent. It was inferred thata fullerene adduct would be produced in the fullerene solutions throughthe above-described step of producing a fullerene adduct, and as aresult, the abrasion resistance improved and the amount of volatilecomponents could be minimized due to the improved abrasion resistance.

Example 4

A lubricating oil composition was obtained in the same manner as inExample 2 except that a fullerene solution was irradiated withultraviolet light 8 times. In Example 4, the fullerene residual rate was0.25 after 8 times of ultraviolet irradiation (5.3 J per milliliter ofthe fullerene solution). Thus, the ultraviolet irradiation was stoppedand the contents were taken out from the quartz cell to obtain alubricating oil composition. The concentration of the fullerene in thelubricating oil composition was measured, and the result was 25 massppm. The fullerene residual rate was 0.25. The results of the degree ofdesorbed gas and the abrasion resistance of the obtained lubricating oilcomposition are shown in Table 1.

As shown in Table 1, in Example 4, when the fullerene solution wasirradiated with ultraviolet light 8 times, the diameter of the rubbingsurface was 155 μnn and the degassing degrees of the lubricating oilcomposition before and after the abrasion resistance test wererespectively 0.1 and 0.3. That is, it was found that the abrasionresistance and the stability under high vacuum were superior.

In addition, when comparing Example 4 with Example 2, both the abrasionresistance and degree of desorbed gas after the abrasion resistance testin Example 4 were superior to those of Example 2. Examples 2 and 4 havethe same conditions except that the number of times of ultravioletirradiation is different. Accordingly, it is estimated that, in Examples2 and 4, the types of cleaved molecules (additional groups of fullereneadduct) produced are almost the same as each other, and the differenceis that the fullerene residual rate of Example 4 is lower than that ofExample 2, that is, a larger amount of the fullerene adduct was producedin Example 4. It is inferred that, due to this difference, the abrasionresistance would be improved in Example 4, and as a result, the degreeof desorbed gas after the abrasion resistance test would also belowered.

Example 5

A lubricating oil composition was obtained in the same manner as inExample 1 except that irradiation using a low-pressure mercury UV lamp(Sen Lights Co., Ltd., model UVL20PH-6 including ultraviolet light at185 nm and 254 nm as light wavelength components) as a light source ofradiation was performed for 20 seconds. Here, the irradiation range was5 cm², and the output was 0.2 W/cm². That is, the lubricating oilcomposition was irradiated with 20 J of ultraviolet light (7 J permilliliter of a fullerene solution) for 20 seconds. The concentration offullerene in the lubricating oil composition was measured, and theresult was 22 mass ppm and the fullerene residual rate was 0.22. Theresults of the degree of desorbed gas and the results of the abrasionresistance of the obtained lubricating oil composition are shown inTable 1.

Example 6

A lubricating oil composition was obtained in the same manner as inExample 1 except that X-ray irradiation was performed for 480 secondsusing an X-ray irradiation device (Toreck Co., Ltd., R1X-250C-2) as alight source of radiation. The concentration of fullerene in theobtained lubricating oil composition was measured, and the result was 20mass ppm and the fullerene residual rate was 0.20. The degree ofdesorbed gas and the abrasion resistance of the obtained lubricating oilcomposition are shown in Table 1.

When comparing Example 5 with Example 4, both were subjected toultraviolet irradiation, and as a result, the fullerene residual ratewas lowered to the same extent. However, the abrasion resistance and thedegree of desorbed gas after the abrasion resistance test in Example 4were superior to those of Example 5. It is inferred that this is becauselight (far ultraviolet light) at 185 nm would be included in ultravioletlight in Example 5.

When comparing Example 6 with Example 5, both were subjected toirradiation, and as a result, the fullerene residual rate was lowered tothe same extent. However, the abrasion resistance and the degree ofdesorbed gas after the abrasion resistance test in Example 6 wereinferior to those of Example 5. It is inferred that this is becauseX-rays having higher energy than ultraviolet light were used asradiation in Example 6.

Example 7

A lubricating oil composition was obtained in the same manner as inExample 1 except that1-butyl-3-methyl-imidazolium-bis(trifluoromethanesulfonyl)imide(manufactured by Tokyo Chemical Industry Co., Ltd., LiTFS1), which is anionic liquid, was used as a base oil. The results of the degree ofdesorbed gas and the abrasion resistance of the obtained lubricating oilcomposition are shown in Table 1.

Comparative Example 3

A lubricating oil composition was obtained in the same manner as inExample 7 except that raw material fullerene (without sublimation step)was used as it is instead of the fullerene sublimate. The results of thedegree of desorbed gas and the abrasion resistance of the obtainedlubricating oil composition are shown in Table 1.

When comparing Example 7 with Comparative Example 3, Example 7 in whichthe fullerene sublimate was used had excellent degrees of desorbed gasbefore and after the abrasion resistance test.

Example 8

A lubricating oil composition was obtained in the same manner as inExample 3 except that1-decyl-3-methyl-imidazolium-bis(trifluoromethanesulfonyl)imide(manufactured by Tokyo Chemical Industry Co., Ltd.), which is an ionicliquid, was used as a base oil. The concentration of fullerene in thelubricating oil composition was measured, and the result was 12 mass ppmand the fullerene residual rate was 0.12. The degree of desorbed gas andthe abrasion resistance of the obtained lubricating oil composition areshown in Table 1. The degree of desorbed gas and the abrasion resistanceof the obtained lubricating oil composition are shown in Table 1.

Example 9

A lubricating oil composition was obtained in the same manner as inExample 4 except that1-decyl-3-methyl-imidazolium-bis(trifluoromethanesulfonyl)imide(manufactured by Tokyo Chemical Industry Co., Ltd.), which is an ionicliquid, was used as a base oil. The concentration of fullerene in thelubricating oil composition was measured, and the result was 35 mass ppmand the fullerene residual rate was 0.35. The degree of desorbed gas andthe abrasion resistance of the obtained lubricating oil composition areshown in Table 1. The degree of desorbed gas and the abrasion resistanceof the obtained lubricating oil composition are shown in Table 1.

Comparison results of Examples 8 and 9 with Example 7 showed the sametendency as the above-described comparison results of Examples 3 and 4with Example 1. That is, it was found that the ultraviolet irradiationtreatment and the heat treatment were effective even in different baseoils from the viewpoints of the abrasion resistance effects andreduction of degassing.

Example 10

A lubricating oil composition was obtained in the same manner as inExample 1 except that1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide, which is an ionicliquid, was used as a base oil. The degree of desorbed gas and theabrasion resistance of the obtained lubricating oil composition areshown in Table 1.

Comparative Example 4

A lubricating oil composition was obtained in the same manner as inExample 10 except that raw material fullerene (without sublimation step)was used as it is instead of the fullerene sublimate. The results of thedegree of desorbed gas and the abrasion resistance of the obtainedlubricating oil composition are shown in Table 1.

When comparing Example 10 with Comparative Example 4, Example 10 inwhich the fullerene sublimate was used had superior degrees of desorbedgas before and after the abrasion resistance test than ComparativeExample 5.

Example 11

A lubricating oil composition was obtained in the same manner as inExample 3 except that1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide, which is an ionicliquid, was used as a base oil. The concentration of fullerene in thelubricating oil composition was measured, and the result was 18 mass ppmand the fullerene residual rate was 0.18. The degree of desorbed gas andthe abrasion resistance of the obtained lubricating oil composition areshown in Table 1.

Example 12

A lubricating oil composition was obtained in the same manner as inExample 4 except that1-ethyl-3-methylimidazolium-bis(fluorosulfonyl)imide, which is an ionicliquid, was used as a base oil. The concentration of fullerene in thelubricating oil composition was measured, and the result was 40 mass ppmand the fullerene residual rate was 0.40. The degree of desorbed gas andthe abrasion resistance of the obtained lubricating oil composition areshown in Table 1.

Comparison results of Examples 11 and 12 with Example 10 showed the sametendency as the above-described comparison results of Examples 8 and 9with Example 7. That is, it was found that the ultraviolet irradiationtreatment and the heat treatment were effective even in different ionicliquids from the viewpoints of the abrasion resistance results andreduction of degassing.

Example 13

A lubricating oil composition was obtained in the same manner as inExample 1 except that1-butyl-4-methyl-pyridium-bis(fluorosulfonyl)imide, which is an ionicliquid, was used as a base oil. The degree of desorbed gas and theabrasion resistance of the obtained lubricating oil composition areshown in Table 1.

Comparative Example 5

A lubricating oil composition was obtained in the same manner as inExample 13 except that raw material fullerene (without sublimation step)was used as it is instead of the fullerene sublimate. The degree ofdesorbed gas and the abrasion resistance of the obtained lubricating oilcomposition are shown in Table 1.

When comparing Example 13 with Comparative Example 5, Example 13 inwhich the fullerene sublimate was used had excellent degrees of desorbedgas before and after the abrasion resistance test. This was the same asthe above-described comparison result of Example 1 with ComparativeExample 1 and the above-described comparison result of Example 7 withComparative Example 3. That is, it was found that use of fullerenesublimate was effective even in different base oils from the viewpointof reducing the degree of desorbed gas.

INDUSTRIAL APPLICABILITY

According to the present invention, it is possible to provide alubricating oil composition which has a low vapor pressure and in whichexcellent abrasion resistance can be exhibited, an increase in vaporpressure due to deterioration of a base oil can be suppressed, andlubricating performance can be stably maintained over a long period oftime even under vacuum.

The lubricating oil composition of the present embodiment is suitablefor various oils such as: industrial gear oil; hydraulic oil; compressoroil; refrigerator oil; cutting oil; plastic working oils such as rollingoil, pressing oil, forging oil, drawing oil, drawing oil, and punchingoil; metal working oils such as heat treatment oil and electricdischarge machining oil; sliding guide surface oil; bearing oil;rust-proof oil; and heat medium oil. In particular, the lubricating oilcomposition thereof is suitable as various oils used in vacuum states,that is, used in outer space or in vacuum containers provided in vacuumapparatuses.

In addition, the lubricating oil composition of the present invention isuseful for devices and equipment used in high altitude regions or outerspace. For example, the lubricating oil composition thereof issignificantly useful for long-term suppression of damage or abrasion ofmetal parts under vacuum in, for example, sliding portions of devices orequipment mounted on aircraft, spacecraft, rockets, probes, spacestations, and satellites. In addition, the lubricating oil compositionof the present invention is significantly useful for long-termsuppression of damage or abrasion of metal parts in sliding portions ofvacuum containers provided in vacuum apparatuses such as a vacuummetallurgical device for forging, joining, or the like, a vacuumchemical device for performing a chemical reaction or the like, a vacuumthin film-forming/processing device for vapor deposition, sputtering, orthe like, an analyzer such as an electron microscope, and a vacuum testdevice for performing bending/tensile/compression tests or the like.

1. A lubricating oil composition, comprising: a fullerene and a baseoil, wherein the fullerene is a fullerene sublimate, and wherein thebase oil is a multiply alkylated cyclopentane oil or an ionic liquid. 2.The lubricating oil composition according to claim 1, furthercomprising: a fullerene adduct, wherein the fullerene adduct has astructure in which an additional group has been added to the fullerene,wherein the additional group has a part of a molecular structure whichconstitutes the base oil.
 3. A method for producing the lubricating oilcomposition according to claim 1, the method comprising: a dissolutionstep of dissolving a fullerene sublimate in a base oil to obtain afullerene solution.
 4. The method for producing a lubricating oilcomposition according to claim 3, the method further comprising: asublimation step of sublimating and vaporizing a raw material fullerenein a non-oxidizing atmosphere, and then cooling and solidifying thevaporized fullerene to obtain the fullerene sublimate, before thedissolution step.
 5. The method for producing a lubricating oilcomposition according to claim 3, wherein the fullerene sublimatecontains C₆₀ or C₇₀ or a mixture thereof.
 6. The method for producing alubricating oil composition according to claim 3, the method furthercomprising: a removal step of removing insoluble components from thefullerene solution after the dissolution step.
 7. The method forproducing a lubricating oil composition according to claim 3, the methodfurther comprising: a heat treatment step of subjecting the fullerenesolution to a heat treatment in a non-oxidizing atmosphere after thedissolution step to produce a fullerene adduct.
 8. The method forproducing a lubricating oil composition according to claim 7, wherein atemperature during the heat treatment in the heat treatment step iswithin a range of higher than an upper limit usage temperature of thebase oil and lower than or equal to the upper limit usage temperature+200° C.
 9. The method for producing a lubricating oil compositionaccording to claim 7, wherein a temperature of the heat treatment in theheat treatment step is 150° C. to 300° C.
 10. The method for producing alubricating oil composition according to claim 3, the method furthercomprising: a radiation treatment step of irradiating the fullerenesolution with radiation in a non-oxidizing atmosphere after thedissolution step to produce a fullerene adduct, wherein the radiation isultraviolet light or ionizing radiation.
 11. The method for producing alubricating oil composition according to claim 10, wherein the radiationis ultraviolet light having a wavelength of 190 nm to 365 nm.
 12. Themethod for producing a lubricating oil composition according to claim10, wherein the amount of energy of the radiation emitted in theradiation treatment step is 1 J to 100 J per milliliter of the fullerenesolution.
 13. The method for producing a lubricating oil compositionaccording to claim 7, wherein an oxygen partial pressure in thenon-oxidizing atmosphere is less than or equal to 10 pascals.
 14. Themethod for producing a lubricating oil composition according to claim 7,wherein the heat treatment step or the radiation treatment step isperformed until a concentration of the fullerene in the fullerenesolution is 0.1 times to 0.7 times a concentration of the fullereneobtained before the heat treatment step or the radiation treatment step.15. The method for producing a lubricating oil composition according toclaim 14, wherein a treatment time of the heat treatment step or theradiation treatment step is 5 minutes to 24 hours.
 16. A vacuumapparatus, comprising: a vacuum container in which the lubricating oilcomposition according to claim 1 is used.
 17. The lubricating oilcomposition according to claim 1, wherein the fullerene consists of thefullerene sublimate, and the base oil consists of the multiply alkylatedcyclopentane oil or the ionic liquid.
 18. The lubricating oilcomposition according to claim 1, wherein a concentration of thefullerene sublimate in the lubricating oil composition is 0.0001 mass %to 0.010 mass %, and an amount of the base oil in the lubricating oilcomposition is 90.0000 mass % to 99.9999 mass %.